Metal oxides and in particular manganese oxides (MnO2) have found several uses in several practical applications such as primary batteries, rechargeable batteries, electromagnetic radiation absorption, catalyst, antibacterial effect and sterilization applications. Until recently only micrometer scales particles have been used but some studies indicate that applying sub micrometer scale particles, i.e., oxide nanoparticles several advantages over larger particles can be obtained. Known synthesis and manufacturing methods of making oxide nanoparticles are described to be chemical precipitation, hydrothermal precipitation, flame pyrolysis and mechanical grinding.
Various types of manganese dioxides (MnO2) have been employed as catalysts and especially as electroactive materials in electrochemical capacitors and batteries. This is due to their great abundance, low cost, favorable charge density, high electrochemical and chemical stability and low toxicity. The modern electronic devices, such as digital cameras and cordless tools, require batteries to be better suited for the high-power application. Despite of significant advances in the development and commercialization of new battery systems, the alkaline Zn/MnO2 battery still occupies a major battery market share due to its favorable cost and low toxicity. However, the current commercial alkaline Zn/MnO2 battery that uses electrolytic manganese dioxide as cathode cannot meet the requirements of the new generation of electronic devices in high rate performance. For example, only 30%-40% of the active cathode material in an alkaline Zn/MnO2 battery is utilized in a high-power electronic device.
Therefore, it is necessary to improve the high rate performance of the alkaline Zn/MnO2 battery for the development of new electronic devices.
There are many factors that affect the performance of the alkaline Zn/MnO2 battery. The nature of the cathode plays an important role in the limitation of the performance of the battery compared to other factors. The active material of a cathode used in current alkaline Zn/MnO2 battery is electrolytic manganese dioxide (EMD). The commercial EMD has a relatively small specific surface area (about 40 m2/g). The low specific surface area limits the contact area between the electrolyte and MnO2, leading to a low utilization and rate capacity, especially at a high rate condition. Therefore, increasing the specific surface area of MnO2 is an effective way to improve the performance of the Zn/MnO2 battery. Nanoscale materials have special physical and chemical properties and nanostructure provides the materials with a large surface area. Nano manganese dioxide can be used for various applications, such as molecule/ion sieves, catalysts, magnetic materials, battery materials, supercapacitors, and cathodic electrocatalysts for fuel cells.
A second factor that affects the performance of the alkaline Zn/MnO2 battery is the crystalline phase of the EMD. Manganese oxide has several crystalline phases and ability to control the crystalline phases while simultaneously achieving nanoscale materials is challenging. Up to now, many methods have been proposed for the preparation of nano manganese oxide, including simple reduction, coprecipitation, thermal decomposition, and sol-gel processes. These methods are complicated, usually under wild conditions, and the specific surface area of the products is not much larger than that of the commercial EMD. However, until now EMD cannot produce free and aggregate free nano particulate powders.
The cathode materials for Li-ion batteries are usually oxides of transition metals due to their high electrochemical potentials during highly reversible lithium insertion/deinsertion. There is literature available on the preparative, structural, and electrochemical studies of oxides of Co, Ni, Mn, and V with regard to lithium battery cathodes. Recently, nanoparticles have been suggested as electrode materials for Li batteries. Possible advantages of nanoparticles as active mass in electrodes for Li batteries may relate to high rate capability. Since the rate-determining step in Li insertion electrodes is supposed to be solid-state diffusion (Li ions in the bulk of the active mass), the smaller the particles, the smaller is the diffusion length, and the electrode's kinetics are expected to be faster. The utility of MnO2 compounds in lithium rechargeable batteries was discussed extensively in the past and has also been demonstrated in commercial rechargeable lithium batteries. Reversible Li insertion around 4.1 V (vs Li/Li+), abundance of manganese in the earth's crust, and relatively low toxicity are the advantages of the LiMn2O4 spinel as compared to lithiated cobalt and nickel oxides. Synthetic routes leading to the formation of LiMn2O4 published so far include a calcination step at high elevated temperature for long time period as a major and critical step. These methods produce microparticles.
Metal oxide particles find also applications in radiofrequency such as microwave absorption. Microwaves are electromagnetic waves with a frequency range in the electromagnetic spectrum of 300 MHz to 300 GHz. However, most applications of microwave technology make use of frequencies in the range of 1-40 GHz. With the rapid advancements in wireless communications the density of radiofrequency waves and microwaves in our surroundings is becoming a serious problem. Electronic devices such as personal hand phones and personal computers emit electromagnetic waves, causing serious electromagnetic interference phenomena and resulting in wave pollution problems. In order to prevent such phenomena, electromagnetic (EM) waves absorbing materials are generally used.
The use of electromagnetic absorbers can ease this problem and, therefore, absorbers of electromagnetic waves are becoming increasingly important for applications outside special fields like silent rooms, radar systems and military applications. Promising electromagnetic wave absorbers have been widely investigated to eliminate the above problems; in particular, an absorber with a plate structure has become the focus of study because of its practical and simple preparation method. Manganese dioxide (MnO2) is also one of the raw materials of manganese ferrite, which has wide application in military and civil engineering for its excellent wave absorbing performance in lower frequency bands. However, to the best of our knowledge, there are no reported results on the electromagnetic characteristic and wave absorbing mechanism of MnO2 nanoparticulate and in particular electrolytically produced and agglomerate free MnO2 nanoparticle powders.
Beyond above-mentioned electrical applications metal oxide nanoparticles such as MnO2 can also find applications in antibacterial applications due to their high oxidation capability to disrupt the integrity of the bacterial cell envelope through oxidation similar to other antibacterial agents such as ozone and chlorine.
Background art is represented by US 2013199673, CN 102243373, US2012093680 and